Illuminants are understood in the present case as sources of optical radiation lying in the visible, ultraviolet, or infrared spectra, which are operated using electrical energy.
In principle, it is desirable to cause illuminants to illuminate very brightly with an acceptable power consumption. It has already been proposed that a gas volume be excited enough by supplying high-frequency electrical energy such that a luminescent plasma arises.
A device for plasma excitation using microwaves is known from DE 103 35 523 B4, in which a microwave conductor feed line branches and stud electrodes are formed therein, the length of which results in a microwave phase shift.
A plasma generation device which uses microwaves is also known, for example, from U.S. Pat. No. 4,908,492. A cylindrical HF conductor arrangement having a cylindrical outer conductor and a helical inner conductor, between which microwave energy is supplied is proposed therein. A discharge tube is to be arranged within the helical coil. Restrictions with respect to the dimensions and the shape are to be eliminated and a sufficient amount of power is to be coupleable into the gas or plasma, respectively. The use as a light source of high brightness and short wavelength for the purposes of optical reactions is mentioned.
A discharge tube arrangement having an excitation device and having a discharge tube is known from U.S. Pat. No. 5,072,157, which is formed from light-transmissive, dielectric material. The excitation device is designed for the purpose of exciting surface waves in the filling of the discharge tube. At least one impedance adaptation network is provided between a decoupling point and a high-frequency power source.
A device is known from U.S. Pat. No. 4,049,940, which is considered to be the closest prior art, in which a plasma is generated in a gas column by excitation of a surface wave using high-frequency energy. The surface wave generation means for the high-frequency energy coupling only extends over a part of the gas column and that such power is provided in the exciting electrical field that the generated plasma extends beyond the corresponding part of the gas column. In one exemplary embodiment, the gas column is contained in an elongated, insulated housing, wherein a first metallic tube, which is open on both sides, and a second tube, which encloses the first, so that a coaxial arrangement is obtained, are provided.
The microwave excitation of the gas volumes in illuminants according to the prior art is advantageous and desirable per se, because high luminances can thus be achieved, for example. However, it is disadvantageous that typically the use of resonant structures is necessary, which opposes the operation using more cost-effective broadband energy sources; in addition, shading of the light volume is often caused by the surrounding structures, or shielding of the coupled high-frequency energy is necessary, respectively.
It is desirable to at least partially remedy at least a part of the mentioned problems.